Alignment: fixed fitting of Detector translation, due to first element having to being 0

Thanks Christian for spotting this
Signed-off-by: Nicola VIGANÒ <nicola.vigano@esrf.fr>

nabu/preproc/alignment.py

@@ -682,20 +682,21 @@ class DetectorTranslationAlongBeam(AlignmentBase):
 
         if use_adjacent_imgs:
             shifts_vh = np.cumsum(shifts_vh, axis=0)
-        img_pos_increments = img_pos[1:] - img_pos[0]
+
+        img_shifts_vh = np.concatenate(([[0, 0]], shifts_vh), axis=0)
 
         # Polynomial.fit is supposed to be more numerically stable than polyfit
         # (according to numpy)
-        coeffs_v = Polynomial.fit(img_pos_increments, shifts_vh[:, 0], deg=1).convert().coef
-        coeffs_h = Polynomial.fit(img_pos_increments, shifts_vh[:, 1], deg=1).convert().coef
+        coeffs_v = Polynomial.fit(img_pos, img_shifts_vh[:, 0], deg=1).convert().coef
+        coeffs_h = Polynomial.fit(img_pos, img_shifts_vh[:, 1], deg=1).convert().coef
 
         if self.verbose:
             f, axs = plt.subplots(1, 2)
-            axs[0].scatter(img_pos_increments, shifts_vh[:, 0])
-            axs[0].plot(img_pos_increments, polyval(img_pos_increments, coeffs_v))
+            axs[0].scatter(img_pos, img_shifts_vh[:, 0])
+            axs[0].plot(img_pos, polyval(img_pos, coeffs_v))
             axs[0].set_title("Vertical shifts")
-            axs[1].scatter(img_pos_increments, shifts_vh[:, 1])
-            axs[1].plot(img_pos_increments, polyval(img_pos_increments, coeffs_h))
+            axs[1].scatter(img_pos, img_shifts_vh[:, 1])
+            axs[1].plot(img_pos, polyval(img_pos, coeffs_h))
             axs[1].set_title("Horizontal shifts")
             plt.show(block=False)
 

nabu/preproc/tests/test_alignment.py

@@ -35,7 +35,7 @@ def bootstrap_dtr(request):
     cls.align_images = align_imgs - dark_img
     cls.img_pos = (1 + np.arange(6)) * 0.01
 
-    cls.expected_shifts_vh = np.array((311.25, 308.9))
+    cls.expected_shifts_vh = np.array((129.93, 353.18))
 
     cls.reference_shifts_list = [
         [-9.39, 11.29],